Fire retardant foup wafer carrier

ABSTRACT

A fire retardant container for semiconductor wafers having an enclosure portion formed from polycarbonate plastic. The enclosure has a top, a bottom, a pair of opposing sides, a back, and an open front. The container includes a door to close the open front having an outer surface portion formed from a plastic material having a flame propagation index of not greater than 9.0 (m/s  1/2 )(kW/m) −2/3 .

FIELD OF THE INVENTION

[0001] This invention relates to wafer carriers. More particularly itrelates to fire retardant wafer carriers.

BACKGROUND OF THE INVENTION

[0002] Processing of semi-conductor wafers into finished electroniccomponents typically requires many processing steps where the wafersmust be handled and processed. The wafers are very valuable, and areextremely delicate and easily damaged by physical and electrical shocks.In addition, successful higher yield processing requires the utmost incleanliness, freedom from particulates and other contaminants. As aresult, specialized containers or carriers have been developed for useduring processing, handling and transport of wafers. These containersprotect the wafers from physical and electrical hazards, and aresealable to protect the wafers from contaminants. Such wafer carriers orcontainers generally comprise an enclosure having a number of waferholding shelves inside. One side of the container is open for access,and is closed by a door.

[0003] The semiconductor industry is in the process of evolvingfabrication facilities to use wafers having a diameter of 300 mm. Thewafer carriers used for 300 mm wafers are normally configured as a FrontOpening Unified Pod (FOUP). Examples of FOUP wafer carriers aredisclosed in U.S. Pat. Nos. 6,010,008, 6,082,540, 6,206,196, 6,216,874and 6,267,245, each commonly owned by the assignee of the presentinvention, and each of which is fully incorporated herein by reference.

[0004] The enclosure for wafer carriers and containers has typicallybeen formed from polycarbonate plastic material. While polycarbonate hasthe advantages of relatively easy formability and high impactresistance, it is also a relatively flammable material that readilypropagates flame. Free burn testing involving an array of only fourpolycarbonate FOUP wafer carriers has shown peak heat release rates ofmore than 1 MW. Because as many as 5,000 to 10,000 FOUP wafer carriersmay be stored in a single semiconductor processing facility, there is anon-trivial risk of fire in such facilities associated withpolycarbonate wafer carriers. Not only does fire in a semiconductorprocessing facility pose a risk of significant property loss and hazardsto the life safety of occupants in the facility, even a small fire maycause extreme disruption to the semiconductor production process due tocontamination from airborne particulates and combustion products. Thus,while there have been no known fire losses to date from a wafer carrierfire, the potentiality and possible consequences of such an event makeimprovements to fire safety associated with wafer carriers highlydesirable.

[0005] Wafer carriers are often stored in multi-tier storage racks knownas “stockers”. In a stocker, FOUP wafer carriers are stored side-by-sidein vertically stacked tiers. These stockers are typically arranged inopposing fashion across an aisle, from which they may be accessed byrobotic equipment. Each stocker may be multi-floors high and may containhundreds of FOUPs. While vertical stacking offers an efficient means ofstoring many types of devices and materials, including wafer carriers,it is well known that stacked arrangements of flammable materialspresent a heightened fire protection concern. This is due to the generaltendency of fire to propagate more readily vertically through buoyantmotion of pyrolysis products. In addition, fixed fire sprinklerprotection covering all areas of stacked material is often verydifficult and expensive to achieve. As a result, in order to minimizethe size and rate of fire growth in a vertical storage arrangement, oneimportant fire protection strategy is to retard, or preferably evenprevent, the vertical propagation of fire from material in one tier ofstorage to next tier that is immediately vertically adjacent. To theextent that propagation of a fire beyond the area of ignition can beslowed, more time is provided for detection and suppression of the firein its incipient stages, thus minimizing damage and process disruption.

[0006] Two important variables that can have a significant effect onfire propagation in vertical storage are the geometry of the storeditems and the flame propagation characteristics of the materialcomposition of the items. In common fire protection engineeringpractice, these variables may sometimes be altered so as to obtain anoptimal result from a fire protection standpoint. Wafer carriers,however, present a unique challenge in this regard in that therequirements of the semiconductor industry for wafer carriers are verystringent and process critical. For instance, in a FOUP wafer carrier,there are over 200 precise dimensions required to hold wafers in placerepeatably, and there are also stringent material standards formechanical strength, structural integrity, and chemical stability of thematerials used in the carrier. Any modifications made to carriers forthe purposes of fire safety must not compromise these standards. Becauseof these difficulties, previous efforts to improve the fire safety ofwafer carriers, both existing and new, have proceeded slowly and havenot produced significant changes in wafer carrier design to date.

[0007] What is still needed is some type of apparatus or method forimproving the fire safety of new and existing wafer carriers stacked ina multi-tier stocker.

SUMMARY OF THE INVENTION

[0008] The present invention is a front opening unified pod wafercontainer comprising an enclosure portion formed substantially frompolycarbonate plastic having at least a top, a bottom, a pair ofopposing sides, a back, and an open front, and a door to close the openfront. The door has an outer surface portion formed substantially from aplastic material having a Fire Propagation Index of not greater than 9.0(m/s ^(1/2))(kW/m)^(−2/3). Suitable plastic materials include polyimide,polyether imide, polyamide imide, polyketone, polyetherketone,polyetheretherketone, polyetherketoneketone, polyether sulphone, andpolytetrafluoroethylene. The invention may also be characterized as amethod of making a fire retardant wafer container and as a method ofretrofitting an existing wafer container to improve its fire retardancy.

[0009] The present invention recognizes meets the need for a wafercontainer that is resistant to the vertical propagation of fire,especially when multiple wafer containers are stored in a verticalstocker arrangement. In addition, the present invention permits the useof less-expensive, more easily formable, polycarbonate plastic for thecontainer, while still offering resistance to the vertical propagationof fire.

[0010] Additional objects, advantages, and novel features of theinvention will be set forth in part in the description which follows,and in part will become apparent to those skilled in the art uponexamination of the following or may be learned by practice of theinvention. The objects and advantages of the invention may be realizedand attained by means of the instrumentalities and combinationsparticularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is an elevation view of a plurality of wafer carriersarrayed in stockers.

[0012]FIG. 2 is a perspective view of a FOUP wafer carrier.

[0013]FIG. 3 is an elevation view of a wafer carrier door according to apreferred embodiment of the present invention.

[0014]FIG. 4 is a perspective, partially exploded view of an alternativeembodiment of a FOUP wafer carrier and door according to the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The accompanying Figures depict embodiments of the wafercontainer of the present invention, and features and components thereof.Any references to front and back, right and left, top and bottom, upperand lower, and horizontal and vertical are intended for convenience ofdescription, not to limit the present invention or its components to anyone positional or spacial orientation. Any dimensions specified in theattached Figures and this specification may vary with a potential designand the intended use of an embodiment of the invention without departingfrom the scope of the invention.

[0016] In FIG. 1, there is shown a simplified elevation view of aplurality of FOUP wafer carriers 100 arrayed in typical verticalstockers 150. A typical semiconductor processing facility may havemultiple rows of stockers 150 arranged in parallel fashion with aisles180 between the rows as shown. Robotic handling equipment may be used inaisles 180 to transfer wafer carriers 100 to and from stockers 150.Within each stocker 150, wafer carriers 100 are supported side-by-sideby horizontal supports 160, forming vertically stacked tiers 162 ofwafer carriers 100. Wafer carriers 100 are normally arranged in stockers150 so that the door of the carrier faces outward into aisle 180.

[0017] Referring to FIG. 2, each FOUP wafer container 100 has anenclosure portion 102, constructed of polycarbonate plastic, and havinga top 104, a bottom 106, a pair of opposing sides 108 and 110, and aback 112. A door 114 closes the open front 116 of the enclosure portion102, fitting into door recess 118. Wafer supports 122 are provided tosupport semi-conductor wafers within the enclosure. Kinematic coupling124, mounted to the exterior surface of enclosure bottom 106 is providedto facilitate automated handling of the container during use and toprovide a reference datum for locating the wafers in the housing duringprocessing. Robotic lifting flange 126 is mounted on the exteriorsurface of enclosure top 104 and is provided to facilitate automatedhandling and transport of container 100 during use.

[0018] As may be seen from reference now to FIGS. 1 and 2, verticalpropagation of fire within stockers 150 can be retarded between tiers162 at the sides 108, 110 and back 112 of wafer carriers 100 byproviding solid portions in horizontal supports 160, blocking anyvertical openings between tiers. At the front, however, doors 114 arevertically aligned, forming a pathway for vertical propagation of firebetween tiers 162.

[0019] It is known in the art to classify materials according to therelative propensity of the materials to propagate fire. One suchclassification, considered particularly indicative of the firepropagation behavior of materials under highly radiative flameconditions prevalent in large scale fires, uses a Fire Propagation Index(FPI) value that is determined for the material. To determine the FPI ofa material, the material is tested according to methods well known inthe art to determine a peak chemical heat release rate per unit width(Q′_(ch)), and a Thermal Response Parameter (TRP), which is calculatedaccording to the relation:

TRP=ΔT_(lg){square root}{square root over (kρc_(p))}

[0020] where ΔT_(lg) is the ignition temperature of the material aboveambient in K°, k is the material thermal conductivity in kW/m-K°, ρ isthe material density in g/m³, and c_(p) is the material specific heat inkJ/g-K°. The FPI may then be calculated according to the relation:${FPI} = {1000\left( \frac{\left( {0.42Q_{ch}^{\prime}} \right)^{\frac{1}{3}}}{TRP} \right)}$

[0021] Materials may be generally classified according to their FPIvalue. Materials having an FPI of under 7.0 (ms ^(1/2))(kW/m)^(−2/3) areclassified as Group N-1 “Non-Propagating” materials, those having an FPIof less than 10.0 (m/s ^(1/2))(kW/m)^(−2/3) but at least 7.0 (m/s^(1/2))(kW/m)^(−2/3) are classified as Group D-1 “Decelerating”materials, those having an FPI of between 10.0 (m/s ^(1/2))(kW/m)^(−2/3)and 20.0 (m/s ^(1/2))(kW/m)^(−2/3) are Group 2 “Non-AcceleratingPropagation” materials and those having an FPI of over 20.0 (m/s^(1/2))(kW/m)^(−2/3) are Group 3 “Accelerating Propagation” materials.

[0022] Polycarbonate plastic, as is commonly used for the enclosure anddoors of wafer carriers, normally has a Fire Propagation Index (FPI) ofgreater than about 10.0 (m/s ^(1/2))(kW/m)^(−2/3), which classifies itas a Group 2 or Group 3 fire propagating material. In the invention, atleast the outer surface portion 130 of door 114 of each wafer carrier isformed substantially from a Group N-1 or Group D-1 fire retardantplastic material that has an FPI of 9.0 (m/s ^(1/2))(kW/m)^(−2/3) orless. Although any fire retardant plastic material having an appropriateFPI may be suitable for the purpose, plastics that are known to beacceptable for use in wafer carriers and that have the appropriate FPIare polyimide (PI), polyether imide (PEI), polyamide imide (PAI),polyketone (PK), polyetherketone (PEK), polyetheretherketone (PEEK),polyetherketoneketone (PEKK), polyether sulphone (PES), andpolytetrafluoroethylene (PTFE). The currently most preferred material isPEI having an FPI from between about 8.1 (m/s ^(1/2))(kW/m)^(−2/3) toabout 8.6(m/s ^(1/2))(kW/m)^(−2/3), such as for example, Ultem 1000 madeby GE Plastics, Inc. of Pittsfield, Mass.

[0023] In a preferred embodiment of the invention, at least outersurface portion 130 of door 114 is formed from PEI material. It iscurrently most preferred that the thickness of outer surface portion 130formed from the fire retardant plastic material be at least the typicalthickness of enclosure portion 102, which is generally about 0.3 mm. Itis currently most preferred that outer surface portion 130 is theexterior panel 132 of door 114 alone as shown in FIG. 2, but may also bea separate fire-retardant layer 134 laid over exterior panel 132 of door114 as shown in FIG. 3. Such a fire retardant layer 134 may beovermolded on exterior panel 132, forming a thermal as well as amechanical bond with exterior panel 132, or may be a separate shieldpanel 136 as shown in FIG. 4, attached by any suitable method, includingadhesives or mechanical fasteners. As an alternative, shield panel 136may have structures allowing it to removably “snap” on and off suitablereceiving structures on door 114. Additionally, the outer fire resistantlayer can be a thin film that has been insert molded on the forwardfacing surface of the front door. Other portions of door 114, such asthe chassis 140, latching components, and inner surface 142 may also beformed from the same fire retardant material used for outer surfaceportion 130, and this may serve to improve the overall fire retardancyof wafer carrier 100.

[0024] Existing wafer carriers having doors with polycarbonate outersurfaces may be retrofitted using the apparatus and methods of thepresent invention. Such a retrofit may be accomplished by replacing thepolycarbonate door with a door 114 manufactured according to the presentinvention, or by overlaying exterior panel 132 with shield panel 136 asdescribed above. Such a shield panel may be a flexible sheet materialsuitably adhered to existing door structure.

[0025] Although the discussion above has been focused on FOUP wafercarrier doors, since the doors present the most likely path of verticalpropagation, the methods of the present invention could also be appliedto other vertical surfaces on the wafer carrier. Thus, for example, iffire retardant surfaces are made necessary by openings in horizontalsupports 162 of stocker 150, sides 108, 110 and/or back 112 could bemade with an outer surface of fire retardant plastic as describedherein.

[0026] Although the description above contains many specificities, theseshould not be construed as limiting the scope of the invention but asmerely providing illustrations of some of the presently preferredembodiments of the invention. Thus, the scope of the invention should bedetermined by the appended claims and their legal equivalents, ratherthan by the examples given.

What is claimed is:
 1. A front opening unified pod wafer containercomprising: an enclosure portion formed substantially from polycarbonateplastic having at least a top, a bottom, a pair of opposing sides, aback, and an open front; and a door to close the open front, whereinsaid door has an outer surface portion formed substantially from aplastic material selected from the group of plastic materials consistingof polyimide, polyether imide, polyamide imide, polyketone,polyetherketone, polyetheretherketone, polyetherketoneketone, polyethersulphone, and polytetrafluoroethylene, and wherein said plastic materialhas a Fire Propagation Index of not greater than 9.0 (m/s^(1/2))(kW/m)^(−2/3); whereby the outer surface portion is relativelyretardant to vertical propagation of fire.
 2. The wafer container ofclaim 1, wherein said outer surface portion is formed from polyetherimide plastic.
 3. The wafer container of claim 1, wherein said outersurface portion is formed from polyetheretherketone plastic.
 4. Thewafer container of claim 1, wherein said outer surface portion comprisesan exterior panel of said door.
 5. The wafer container of claim 1,wherein said outer surface portion comprises a layer of fire retardantplastic over a layer of polycarbonate plastic.
 6. The wafer container ofclaim 5, wherein said layer of fire retardant plastic is molded oversaid layer of polycarbonate plastic.
 7. The wafer container of claim 1,wherein said outer surface portion comprises a shield panel affixed tosaid door with an adhesive.
 8. The wafer container of claim 1, whereinsaid outer surface portion comprises a shield panel affixed to said doorwith a plurality of fasteners.
 9. A wafer container comprising: anenclosure portion formed substantially from polycarbonate plastic havingat least a top, a bottom, a pair of opposing sides, a back, and an openfront; and a door to close the open front, wherein said door has anouter surface portion formed from a plastic material having a flamepropagation index of not greater than 9.0 (ms ^(1/2))(kW/m)^(−2/3);whereby the outer surface portion is relatively retardant to verticalpropagation of flame.
 10. The wafer container of claim 9, wherein saidplastic material is selected from the group of plastic materialsconsisting of polyimide, polyether imide, polyamide imide, polyketone,polyetherketone, polyetheretherketone, polyetherketoneketone, polyethersulphone, and polytetrafluoroethylene.
 11. The wafer container of claim10, wherein said plastic material is polyether imide.
 12. The wafercontainer of claim 10, wherein said plastic material ispolyethylethylketone.
 13. The wafer container of claim 9, wherein saidouter surface portion comprises an exterior panel of said door.
 14. Thewafer container of claim 9, wherein said outer surface portion comprisesa layer of fire retardant plastic over a layer of polycarbonate plastic.15. The wafer container of claim 14, wherein said layer of fireretardant plastic is molded over said layer of polycarbonate plastic.16. The wafer container of claim 9, wherein said outer surface portioncomprises a shield panel affixed to said door with an adhesive.
 17. Thewafer container of claim 9, wherein said outer surface portion comprisesa shield panel affixed to said door with a plurality of fasteners.
 18. Amethod of making a flame retardant front opening unified pod wafercarrier comprising: forming, from polycarbonate plastic, an enclosureportion having at least a top, a bottom, a pair of opposing sides, aback, and an open front; and forming a door for closing the open front,said door having an outer surface portion comprising plastic materialwith a Fire Propagation Index of not more than 9.0 (m/s^(1/2))(kW/m)^(−2/3).
 19. The method of claim 18, wherein said door hasan outer panel, and further comprising the step of molding said outersurface portion over said outer panel.
 20. The method of claim 18,wherein said door has an outer panel, and further comprising the stepsof molding a fire retardant layer member and affixing said layer memberto said outer panel.
 21. A method of improving the fire retardancy of afront opening unified pod wafer carrier, said carrier comprising anenclosure portion having at least a top, a bottom, a pair of opposingsides, a back, an open front, and a door to close the open front, allformed substantially from polycarbonate plastic, the method comprisingoverlaying an outer surface of said door with a layer of plasticmaterial having a flame propagation index of not more than 9.0 (m/s^(1/2))(kW/m)^(−2/3).
 22. The method of claim 21, wherein said plasticmaterial is selected from the group consisting of polyimide, polyetherimide, polyamide imide, polyketone, polyetherketone,polyetheretherketone, polyetherketoneketone, polyether sulphone, andpolytetrafluoroethylene, and further comprising the steps of moldingsaid plastic material into a separate shield panel and affixing saidshield panel to said door.
 23. The method of claim 22, wherein saidaffixing step comprises fastening said shield panel to said door with anadhesive.
 24. The method of claim 22, wherein said affixing stepcomprises fastening said shield panel to said door with a plurality offasteners.
 25. A front opening unified pod wafer container comprising:an enclosure portion formed substantially from polycarbonate plastichaving at least a top, a bottom, a pair of opposing sides, a back, andan open front; a door to close the open front, wherein said door has anexterior surface portion; and means for retarding the spread of fire onsaid exterior surface portion.
 26. The wafer container of claim 25,wherein said means for retarding the spread of fire on said outersurface portion comprises an exterior panel of said door, said exteriorpanel being formed from a plastic material having a Fire PropagationIndex of 9.0 (m/s ^(1/2))(kW/m)^(−2/3) or less.
 27. The method of claim26, wherein said plastic material is selected from the group consistingof polyimide, polyether imide, polyamide imide, polyketone,polyetherketone, polyetheretherketone, polyetherketoneketone, polyethersulphone, and polytetrafluoroethylene.
 28. The method of claim 26,wherein said plastic material is polyether imide.
 29. The wafercontainer of claim 25, wherein said door is formed from polycarbonateplastic, and wherein said means for retarding the spread of fire on saidouter surface portion comprises a separate layer of fire retardantplastic material overlaid on said exterior surface portion, said fireretardant plastic material having a Fire Propagation Index of 9.0 (m/s^(1/2))(kW/m)^(−2/3) or less.
 30. The method of claim 29, wherein saidfire retardant plastic material is selected from the group consisting ofpolyimide, polyether imide, polyamide imide, polyketone,polyetherketone, polyetheretherketone, polyetherketoneketone, polyethersulphone, and polytetrafluoroethylene.
 31. The method of claim 29,wherein said plastic material is polyether imide.
 32. The wafercontainer of claim 29, wherein said separate layer of fire retardantplastic material is molded over said exterior surface portion.
 33. Thewafer container of claim 29, wherein said separate layer of fireretardant plastic material is molded as a separate shield panel andaffixed to said exterior surface portion with an adhesive or with aplurality of fasteners.